Compressors



July 19, 1966 K. v. VALBJQRN 3,261,540

COMPRESSORS Filed July 10, 1965 Fig.2c

United States Patent 3,261,540 (IUMFRESSORS Knud Vagn Valhjarn, Nordhorg, Denmark, assignor to Danfoss A/S, Nordhorg, Denmark, a company of Denmark Filed July it), 1963, Ser. No. 294,673

Qiairns priority, application Germany, July 10, 1962,

3 tCiaims. (Cl. 230-19) The present invention relates to the manufacture of reciprocating compressors consisting of at least one cylinder and a piston reciprocating in the cylinder. Such compressors are used, for example, for small refrigerators.

A manufacturer of piston compressors cannot limit himself to one type of a single specific performance, but has to offer a series of compressors with diiferent performance capacities. This different performance capacity was hitherto achieved by a change of the diameter of the piston or a change in the piston stroke, or in some instances by changing both the diameter and stroke. In the first-mentioned case, the piston, the cylinder, and at least some parts of the cylinder head have to be changed. In the second-mentioned case, the crankcase and under given circumstances the cylinder have to be changed. These changes cause rather serious disadvantages. A series of construction elements of different dimensions have to be manufactured and a correspondingly voluminous parts inventory has to be carried. In the case of mass production by means of mechanical production belts, as is usual, for example, for compressors of small refrigerators, the change-over to a type of different performance requires such changes and readjustments, that it is generally preferred to set up a production belt special to each type. This occasions high investment costs. Moreover, there is no possibility, in the case of increased demand for a type of specific performance, to produce beyond the capacity of the corresponding production belts.

According to this invention, all of these disadvantages are eliminated by producing compressors with equal piston stroke and of equal cylinder diameter and varying the displacement volume, corresponding to the desired performance, by means of openings in the cylinder walls at varying distances from the upper dead-center position of the piston and in position to be covered and uncovered by the piston in its reciprocation.

The performance is thus no longer changed by a variation of measurements of individual construction elements, but merely by means of locating openings at different heights relative to the piston surface in upper dead-center position. For all compressors of one series, therefore, there is only need for one set of construction elements, so that the preparation and the stocking of parts become simplified. All types of one series can be manufactured on the same production belt, Without any variation other than a height adjustment of the tool producing the openings in the cylinder walls. In principle, therefore, one production belt alone will be sufficient. Should there be more than one belt available, it is possible, in the event of an increased demand for one type of a particular performance capacity, to transfer that portion which would exceed the production capacity of one belt onto the second production belt. Compressors could even be manufactured in advance and the openings bored later at the heights required by the respective orders.

In setting up a series of compressors, the procedure is that firstly the measurements of the type with the maximum performance are determined. This type can be furnished without additional work. For each type of lesser performance, openings are formed in the cylinder walls at a suitable distance from the upper dead-center to provide the effective displacement required for the performance capacity desired. The location of the openings can easily be determined by calculation or by tests. It has been found that, in this manner, compressors of different ratings can be produced with the type having the lowest performance rating approximately 50% of the type with the highest rating.

It is preferred to make the cross-section of the openings in the cylinder-wall leading to the suction side either equal to or larger than the cross-section of the suction valve, i.e. the cross-section of the opening of the valve during operation. The larger the cross-section of these openings, the smaller is the loss of performance that arises through the sucking in and exhaling of the gases, as long as the openings are uncovered by the piston. In any case, this performance loss can be held lower than the performance gain, which is created through the increase of the degree of utilization of the cylinder volume through the use of such openings.

According to a particularly simple demonstration model, several borings, preferably of equal dimension and at equal heights, are provided around the cylinder circumference for determining the performance of the compressor. Borings have a less weakening effect on the cylinder wall than slits. In order to change the performance, it is merely necessary to adjust to the desired height, the multiple boring tool that encircles the cylinder.

In addition, it is advantageous if the openings are connected with the suction damper. The openings are uncovered by the piston, in some cases, during a relatively long period of the piston-stroke. There is therefore, a danger that noises, especially those of the suction valve, which are isolated from the suction space by means of a damper that communicates with the suction duct, could now travel directly through the openings into the suction space. This danger can be eliminated in the indicated fashion by having the openings open into the suction damper. The invention will be further understood from the following description in connection with the accompanying drawings.

In the drawings:

FIG. 1 is a partial schematic longitudinal sectional view of a compressor manufactured in accordance with the invention,

FIG. 2a is a similar view showing a modification,

FIG. 2b is a P-V-diagram of the embodiment shown in FIG. 2a, and

FIG. 2c is a performance change diagram.

In the construction according to FIG. 1, piston 1 is reciprocated in cylinder 2 by a crank. The upper end of the cylinder is closed by a valve plate 3, which in turn is covered by the valve lid 4. FIG. 1, only suction valve 5 and the suction valve chamber 6 can be seen. The pressure valve, pressure valve chamber, and pressure conduction pipe 7 are placed behind it. Formed integrally with the cylinder are suction mufller chambers 8 which through channels 9 are connected with the suction valve chamber 6. In accordance with the invention, openings 10 are located in the cylinder wall between the upper dead-center T and the lower dead-center T positions of the upper surface of the piston 1. The openings 10 are shown in the form of circular holes bored in the cylinder wall from the outside, so that the access borings 11 in the suction mufflers 8 are made at the same time. The access holes are later plugged. While the number of holes can be varied in accordance with the size and characteristics of the compressor, four equally spaced holes of the same size are illustrated by way of example in FIG. 1. The upper edges Q of these holes are located at a distance y from the upper dead-center T which in accordance with the invention, is varied according to the desired performance rating of the compressor. If the openings and 11 were drilled somewhat lower as indicated in dotted lines at 10 and 11, the performance of the otherwise unchanged compressor would be in: creased. If the openings were omitted altogether, an even higher performance would result. It will thus be seen that the performance rating of the compressor can be varied over a considerable range merely by varying the position of the openings 10 while the diameter and stroke of the piston remain the same.

FIG. 2a illustrates another embodiment. In this case, cylinder 12, in which piston 13 moves back and forth, is equipped not with drilled holes, but with lengthwise slits 14. The valve plate is shown schematically.

The P-V-diagram shown in FIG. 2b belongs to the embodiment of FIG. 2a, P representing the compression pressure and P the suction pressure. The portion of this diagram within the effective piston stroke designated by the distance y, corresponds in general with that of a usual compressor with unbroken cylinder wall and a total piston stroke equal to y. In the area a where the openings 14 are uncovered by the piston, the diagram consists of two somewhat parallel branches, which run very closely above and below respectively to line P The loss herewith indicated is minimal and amounts to about 1 to 2% of the total compression-performance. This loss, moreover, is compensated by the increase in the degree of utilization of the volume in a more effective way, by permitting the cylinder to fill more completely.

FIG. illustrates how a displacement of the upper edge Q of the openings 14 influences the performance of the compressor. For this purpose, the distance of the upper edge Q to the lower dead-center T has been designated with the letter a while the power or performance rating of the compressor is designated with the letter N. The ordinates of the graph thus represent the change in performance AN with changes in the position of the upper edge of the opening or openings in the cylinder wall. The zero-line aN corresponds to the power N of a compressor with closed cylinder walls and a piston displacement x. It can be seen that with an increased distance a, there is first an increased performance, which is then followed by a performance drop. Of particular interest for the purpose of the present invention, is the portion of the curve below the line aN.

By way of example, if a compressor with a pistondiameter of mm. and a piston stroke of 16 mm. with unbroken cylinder walls gives a performance of H.P., then, by means of drilling holes, for example, 3 holes with 4 mm. diameter, the upper edge of which have a distance cover the performance series of /6, A3, and H.P.

In similar fash-' ion, it is possible with one single smaller compressor to While the invention has been described with reference to preferred examples, it will be understood that modifications or variations may be made Without departing from the concept and spirit of the invention.

What I claim is:

1. A method of producing refrigeration compressor housings for assemblying refrigeration compressors of different capacities from said housings with alike components comprising, providing a plurality of similar compressor housings each having a cylinder of equal dimensions for assembly therein of respective pistons driven reciprocably a given stroke length and having a given top dead center in operation, said housings having at least one chamber defining a suction mufiier and a cylinder wall spacing said suction mufiier from said cylinder, drilling openings in the cylinder Wall of said housings at one axial distance from top dead center in some of said housings and at other axial distances in other of said housings, whereby when a given diameter piston is assembled in each cylinder and reciprocably driven in operation said openings define ports opened and closed by respective pistons and some compressors have different capacities than other of said compressors without differences in stroke length and piston diameters among all of said compressors.

2. A method according to claim 1, in which said housings are drilled from exteriorly thereof through said muffler and into said cylinder, and including plugging openings drilled from exteriorly in said mufiier in drilling into said cylinder of each housing.

3. A method of producing refrigeration compressors of different capacities from similar components comprising, providing a plurality of similar compressor housings each having a cylinder of equal dimensions for assembly therein of respective pistons driven reciprocably a given stroke length and having a given top dead center in operation, said housings having at least one chamber defining a suction mufiier and a cylinder wall spacing said suction muffler from said cylinder, drilling openings in the cylinder wall of said housings at one axial distance from top dead center in some of said housings and at other axial distances in other of said housings, assem blying pistons of equal diameter with said cylinders for reciprocation therein at a given length of stroke, whereby when a given diameter piston is assembled in each cylinder and reciprocably driven in operation said openings define ports opened and closed by respective pistons and some compressors have different capacities than other of said compressors without differences in stroke length and piston diameters among all of said compressors.

References Cited by the Examiner UNITED STATES PATENTS LAURENCE V. EFNER, Primary Examiner. 

1. A METHOD OF PRODUCING REFRIGERATION COMPRESSOR HOUSINGS FOR ASSEMBLING REFRIGERATION COMPRESSORS OF DIFFERENT CAPACITIES FROM SAID HOUSINGS WITH ALIKE COMPONENTS COMPRISING, PROVIDING A PLURALITY OF SIMILAR COMPRESSOR HOUSINGS EACH HAVING A CYLINDER OF EQUAL DIMENSIONS FOR ASSEMBLY THEREIN OF RESPECTIVE PISTONS DRIVEN RECIPROCABLY A GIVEN STROKE LENGTH AND HAVING A GIVEN TOP DEAD CENTER IN OPERATION, SAID HOUSINGS HAVING AT LEAST ONE CHAMBER DEFINING A SUCTION MUFFLER AND A CYLINDER WALL SPACING SAID SUCTION MUFFLER FROM SAID CYLINDER, DRILLING OPENINGS IN THE CYLINDER WALL OF SAID HOUSING AT ONE AXIAL DISTANCE FROM TOP DEAD CENTER IN SOME OF SAID HOUSINGS AND AT OTHER AXIAL DISTANCES IN OTHER OF SAID HOUSINGS, WHEREBY WHEN A GIVEN DIAMETER PISTON IS ASSEMBLED IN EACH CYLINDER AND RECIPROCABLY DRIVEN IN OPERATION SAID OPENINGS DEFINE PORTS OPENED AND CLOSED BY RESPECTIVE PISTONS AND SOME COMPRESSORS HAVE DIFFERENT CAPACITIES THAN OTHER OF SAID COMPRESSORS WITHOUT DIFFERENCES IN STROKE LENGTH AND PISTON DIAMETERS AMONG ALL OF SAID COMPRESSORS. 